Janus is the ancient Roman god who gives January its name and is associated with doorways and beginnings.
Roman tradition connected Janus with transitions, entrances, departures, and time’s changes. He is commonly depicted with two faces, one looking forward and one looking backward. That image later became a familiar symbol for reflecting on the old year while anticipating the new one.
The Latin month name Ianuarius was derived from Janus. January became the first month of the Roman calendar in the calendar reforms associated with the late Roman Republic, although earlier Roman calendars had used different month orders and starting conventions.
Janus is often confused with Saturn because Saturnalia was a major Roman festival in December. Saturn, however, is the deity associated with that festival and with the planet Saturn; he is not the source of January’s name. Janus’s connection is specifically to beginnings and thresholds.